This invention relates to a device for filtering contaminants, such as particulates and vapor phase contaminants, from a confined environment such as electronic or optical devices susceptible to contamination (e.g. computer disk drives) by incorporating multiple filtration functions into a single filter.
Many enclosures that contain sensitive instrumentation must maintain very clean environments in order to operate properly. Examples include the following: enclosures with sensitive optical surfaces, or electronic connections that are sensitive to particulates and gaseous contaminants which can interfere with mechanical, optical, or electrical operation; data recording devices, such as computer hard disk drives that are sensitive to particles, organic vapors, and corrosive vapors; enclosures for processing, transport or storage of thin films and semiconductor wafers; and electronic control boxes such as those used in automobiles and industrial applications that can be sensitive to particles, moisture buildup, and corrosion as well as contamination from fluids and vapors. Contamination in such enclosures originates from both inside and outside the enclosures. For example, in computer hard drives, damage may result from external contaminates as well as from particles and outgassing generated from internal sources. The terms xe2x80x9chard drivesxe2x80x9d or xe2x80x9chard disk drivesxe2x80x9d or xe2x80x9cdisk drivesxe2x80x9d or xe2x80x9cdrivesxe2x80x9d will be used herein for convenience and are understood to include any of the enclosures mentioned above.
One serious contamination-related failure mechanism in computer disk drives is static friction or xe2x80x9cstictionxe2x80x9d. Stiction results from the increased adhesion of a drive head to a disk while the disk is stationary plus increased viscous drag parallel to the head-disk interface. Newer high density disks are more sensitive to contamination-caused stiction because they are smoother and only thin layers of lubricants are present. Contaminants on the disk change the surface energy and the adhesive forces between the head and disk, which cause stiction. Also, vapors that condense in the gap between the head and disk can cause stiction. Further exacerbating these effects are the newer lower energy, lower torque motors being used in smaller disk drives for portable computers.
Another serious contamination-related failure mechanism in computer disk drives is head crashes. Head crashes can occur when particles get into the head disk interface. Newer high density drives have 30 nanometer or less flying heights or spacing between the head and disk during operation and typically have disks rotating 5400 revolutions per minute or greater. Even submicron-sized particles can be a problem, causing the head to crash into the particle or the disk after flying over a particle, bringing the drive to an abrupt failure mode. Particles can also adversely affect data integrity and mechanical a reliability of a drive, sometimes referred to as thermal asperity.
In addition, disk drives must be protected against a large number of contaminants in the surrounding environment that can penetrate the drive. This is true for drives used in small to medium sized computer systems which may not be used in the typical data processing environment and is especially true in drives that are removable and portable to any environment such as disk drives that are used in laptop computers or in Personal Computer Memory Card International Association (PCMCIA) slots.
Filtration devices to keep particles from entering these enclosures are well known. They may consist of a filtration media held in place by a housing of polycarbonate, acrylonitrile butadiene styrene (ABS), or some other material; or they may consist of a filtration media in the form of a self-adhesive disk utilizing a layer or layers of pressure sensitive adhesive. These devices are mounted and sealed over a vent hole in the enclosure to filter particulates from the air entering the drive. Filtration performance depends not only on the filter having a high filtration efficiency but also on having a low resistance to air flow so that unfiltered air does not leak into the enclosure through a gasket or seam instead of entering through the filter. Such filters work well for particulates of external origin, but do not address the problems from vapor phase contaminants.
Combination sorbent breather filters to keep particulates and vapors from entering enclosures are also well known. These can be made by filling a cartridge of polycarbonate, ABS, or similar material with sorbent and securing filter media on both ends of the cartridge. Examples of such filters are described in U.S. Pat. No. 4,863,499 issued to Osendorf (an anti-diffusion chemical breather assembly for disk drives with filter media having a layer impregnated with activated charcoal granules); U.S. Pat. No. 5,030,260 issued to Beck et al. (a disk drive breather filter including an assembly with an extended diffusion path); U.S. Pat. No. 5,124,856 issued to Brown et al. (a unitary filter medium with impregnated activated carbon filters to protect against organic and corrosive pollutants); and U.S. Pat. No. 5,447,695 issued to Brown et al. (Chemical Breather Filter Assembly). Unfortunately, many of these designs are too large and take up too much space in today""s miniaturized drives. They again filter only incoming air of particles and mainly incoming air of vaporous contaminates, although some internal air can also be cleaned from internally generated vaporous contaminates since the filters are inside the drive and these contaminates will diffuse into the adsorbent sections of the filters. None of these filters address cleaning the air of internal particles.
A second combination adsorbent breather filter is also well known that encapsulates the adsorbent material such as an impregnated activated carbon polytetrafluoroethylene (PTFE) composite layer between two layers of filter media and is applied over a hole in the enclosure with a layer of pressure sensitive adhesive. These filters work well and are of a size that can be used in today""s small drives but are typically designed to filter air coming into the drive. Thus, the adsorbent is typically primarily desired to adsorb both organic and corrosive vapors from the outside environment and will filter particulates only from air coming into or leaving the drive. Internally generated vapors can be adsorbed by these filters, but often times they are used in conjunction with another internal adsorbent so they can be smaller in size; therefore, such filters do not contain enough adsorbent to adequately adsorb all the internally generated contaminants. Again, particles are also generated inside the drive and are not typically captured by these filters.
A diffusion tube can be included with either the initial particulate breather filter or an adsorbent breather filter as described in U.S. Pat. No. 5,417,743 by Dauber. Diffusion tubes provide additional protection against vaporous contaminants (including moisture) entering the drive through the breather opening by providing a diffusion barrier in the form of the diffusion tube which creates a tortuous or a longer path for vaporous contaminants to diffuse through before entering the drive enclosure. Diffusion tubes reduce the number of contaminants reaching the interior of the enclosure (and/or the adsorbent depending on the location of the filter) and increase the humidity time constants or time required to reach humidity equilibrium with the environment. As used herein, for convenience, the term xe2x80x9cdiffusion tubexe2x80x9d may refer to either a conventional tortuous path or it may refer to a non-tortuous cavity into which incoming air passes before entering the filter.
Internal particulate filters, or recirculation filters, are also well known. These filters are typically pieces of filter media, such as expanded PTFE membrane laminated to a polyester nonwoven backing material, or xe2x80x9cpillow-shapedxe2x80x9d filters containing electret (i.e., electrostatic) filter media. They are pressure fit into slots or xe2x80x9cCxe2x80x9d channels and are placed in the active air stream such as near the rotating disks in a computer hard disk drive or in front of a fan in electronic control cabinets, etc. Alternatively, the recirculation filter media can be framed in a plastic frame. These filters work well for particulate removal of internally generated particles but do not address the problem of vapor phase contaminants, nor do they provide ultimate protection from external particles entering the drive.
Internal adsorbent filters are also well known. One example is described in U.S. Pat. No. 4,830,643 issued to Sassa et al. This patent teaches a sorbent filter where a powdered, granular or beaded sorbent or sorbent mixture is encapsulated in an outer expanded PTFE tube. This filter is manufactured by W. L. Gore and Associates, Inc., Elkton, Md., and is commercially available under the trademark GORE-SORBER(copyright) module. While this is highly effective at collecting vapor phase contaminants, it is currently only available in large and medium sizes like filter volumes down to about 3 cc. In its present form, this filter is incapable of fully addressing the growing needs for even smaller and more compact sorbent filters, nor is it designed to filter the internal air of particulate contamination. A second well known internal adsorbent assembly incorporates a layer of adsorbent, such as activated carbon/PTFE composite, between an encapsulating filter layer and layer of pressure sensitive adhesive that helps encapsulate the adsorbent as well as provides a means of mounting the adsorbent assembly on an interior wall in the enclosure. Such a filter is described in U.S. Pat. No. 5,593,482 issued to Dauber et al, which also allows for an externally mounted adsorbent assembly with access to the enclosure interior. Again neither of these filters address particulate contaminates. A third internal adsorbent assembly incorporates a layer of adsorbent such as activated carbon/PTFE composite between two layers of filter media or is alternately wrapped in a layer of filter media and can be installed between slots or xe2x80x9cCxe2x80x9d channels much the way a recirculation filter is installed but without much real airflow through the filter. Such a filter is described in U.S. Pat. No. 5,500,038 issued to Dauber et al., and, as with the other filters mentioned, this construction does not provide significant particle capturing capability.
As stated above, all of these internal adsorbent filters work well at adsorbing vapor phase contaminants, but they do not filter particulates very well. They can collect particles by some impaction of particles onto the filter (i.e., by having the larger particles impacting or colliding with the adsorbent filter as particle-laden air speeds around the filters) or by diffusion of particles onto the filter. However, these filters do not perform nearly as well as standard recirculation filters that work by a combination of sieving (mechanically capturing particles too large to pass through the pore structure of the filter), impaction (capturing particle too large to follow the bending air streams around filters or the fibers of the filter), interception (capturing particles that tend to follow the air streams, but are large enough to still intercept a filter fiber or in other words those particles with a diameter equal to or greater than the distance between the fiber and the air stream line), and diffusion (capturing smaller particles buffeted about by air molecules in a random pattern and coming into contact with a filter fiber to become collected). These means of air filtration are much more rigorously described in a book entitled xe2x80x9cAir Filtrationxe2x80x9d by R. C. Brown, published by Pergamon Press initially in 1993.
A commercially available adsorbent recirculation filter, available from The Donaldson Company, incorporates activated carbon beads glued to a nonwoven carrier that is sandwiched between two layers of electret filter material and two layers of plastic support screen. This filter provides some sorbent protection at the sacrifice of some internal particle filtration effectiveness, as this construction appears to increase resistance to air flow to the filter relative to a conventional recirculation filter. The sorbent capability is limited, however, due to, for example, the constraints of the filter size and the blockage of sorbent surface area by the glue holding the carbon to the carrier. Moreover, this filter does not filter particles from air entering the drive.
Another issue in today""s drives is contamination due to corrosive ions such as chlorine and sulfur dioxide. To adsorb these compounds the adsorbent is typically treated with a salt to chemisorb the contaminants. When the filters described in the preceding paragraph were washed in deionized water, large amounts of these salts were released, making it unacceptable to today""s sensitive disk drive environments. An alternative washable adsorbent recirculation filter is described in U.S. Pat. No. 5,538,545 issued to Dauber et al., wherein expanded PTFE membranes or other hydrophobic materials are used to encapsulate the adsorbent. However, these filters still do not filter air as it comes into the drive before it has had a chance to deposit particles and do damage to the drive.
Combinations of several filters having different functions in a single drive have been taught. For example, U.S. Pat. No. 5,406,431, to Beecroft, describes a filter system for a disk drive that includes an adsorbent breather and recirculation filter in specifically identified locations within the drive. Also, U.S. Pat. No. 4,633,349, by Beck et al., teaches a disk drive filter assembly comprising a dual media drum type filter element in a recirculating filter assembly that surrounds a breather filter. Further, U.S. Pat. No. 4,857,087, to Bolton et al., teaches incorporating a breather filter in a recirculation filter housing, but has significantly more parts and incorporates a third filter element complete with housings, aperatures, and gaskets to accomplish this inclusion. The combinations described in these patents either locate the filter components in separate regions of the disk drive or incorporate space-consuming fixtures to orient the component parts within the drives.
As disk drives have become smaller and the prices have declined, there has been a push for simplification and the reduction in the number of parts in a drive to reduce cost and improve performance. Also, as the drives continue to increase in recording data density and capacity, they continue to become more sensitive to particulate and vaporous contamination, such that the existing filtration means often do not meet these ever more demanding filtration requirements.
Accordingly, a primary purpose of the present invention is to provide a new, improved multiple function part that can filter both incoming (external) air and internal recirculating air of particulates.
A further purpose of the present invention is to provide an improved multiple function part that can filter both incoming and internal recirculating air of both particulates and vapor phase contaminants.
A further purpose of the present invention is to provide a multiple function part, as described above, which further incorporates a diffusion tube.
A further purpose of the present invention is to provide a multiple function part, as described above, which further incorporates a gasket to help to seal the disk drive housing.
The present invention is a unitary filter that serves multiple filtration functions within the disk drive. In a first embodiment, the filter incorporates a combination of inlet, or breather, filter and recirculation filter. Alternatively, the filter may incorporate a breather filter, a recirculation filter and a sorbent filter, the sorbent filter providing either active filtration (i.e., air is directed through the adsorbent component as it enters the disk drive through the breather hole or air is directed through the adsorbent component as air is recirculated around the drive) or passive filtration (i.e., air within the disk drive passes along the adsorbent component which is adjacent the normal air flow path in the drive, with no air being specifically directed through a cross-section of the adsorbent) or some combination of the two. Further, a diffusion tube could be included in the filter, or alternatively in a location on the drive housing where the filter is positioned, to provide a combined multi-functional or xe2x80x9call-in-onexe2x80x9d filter assembly which has all of the filtration components which are typically contained in a conventional disk drive. Still further, the multi-functional filter could incorporate a gasket that would still further reduce the components required for assembling finished disk drives.
Not only are the filters of the present invention simple to use and install, but another advantage of such a device is that the filter is low in outgassing and nonvolatile residues as well as low in particulation. In addition, depending on the construction, the filters can have the added benefit that they can be washed with deionized water to remove surface ionic contamination and particulation to improve their suitability for those applications requiring such cleanliness such as in computer disk drives without washing out beneficial treatments such as salts which remove acid gases from the air streams. This washability is accomplished by using hydrophobic filter materials (along with impermeable layers such as adhesives, etc.) to surround the adsorbent layers. xe2x80x9cHydrophobicxe2x80x9d as used in this application means the filter materials have a water (or water with surfactant if one is used) entry pressure sufficient to withstand the conditions of conventional washing steps, such as heating, stirring, ultrasonics, etc.
The filter may comprise a layer or layers of adhesive to adhere the filter to the proper location on the interior or exterior of the drive enclosure wall. The filter may optionally cover an inlet diffusion tube groove in the drive housing, or the filter may optionally fully contain the diffusion tube. A layer or layers of filter media are provided in substantially laminar relation to the adhesive to filter the incoming and recirculating air of particles. A layer or layers of adsorbent media may optionally be provided between the adhesive and filter layers, or between filter media layers, to filter one or both of the incoming and recirculating air streams of vaporous contaminants. Appropriate partitioning of the filter is provided to permit flow channels for inlet air and for recirculating air without the possibility of allowing unfiltered inlet air through the filter.
The present invention consolidates filtration functions which were previously performed by two, three, or more filters into a single filter that functions well, is easy to install, is clean and cleanable. Additionally, further components, such as a gasket or gasket(s) or vibration dampening materials, can be included to further reduce the number of components required for final assembly.
In summary, the present invention provides a compact, clean, low outgassing (i.e., typically less than 20,000 ng/g at 85xc2x0 C. for four hours), low particulating (i.e., typically less than (50) one hundred micron sized particle per square centimeter when tested with a liquid particle counter), unitary breather/recirculation filter that can optionally contain adsorbents and also, optionally, can be washable, particularly if the filter comprises hydrophobic PTFE membranes. The invention can utilize any suitable adsorbent type and be tailored for preferential performance in filtering of air from both internal and external sources for particles as well as hazardous vapor contaminants. As a unitary filter, the multi-functional filter minimizes installation time, as compared to the use of several conventional parts to achieve the required filtration and adsorption. The filter can further be combined with an optional diffusion tube to improve the performance of the breather component. The filter can still further be combined with a gasket to provide a means of sealing the disk drive. The multi-functional filters of the present invention can be used in filters where air is driven by normal convection, by diffusion means, by an auxiliary fan, or some combination thereof.